1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting an uplink frame in a wireless local area network (WLAN).
2. Related Art
In wireless LAN systems, as a method for a plurality of stations (STAs) to share a wireless medium, a distributed coordination function (DCF) may be used. The DCF is based on a carrier sensing multiple access with collision avoidance (CSMA/CA).
Generally, when an STA is operated under the DCF access environment, but that a medium has not been used for longer than a DCF interframe space (DIFS) period (i.e., in the case of being idle), the STA may transmit the medium access control (MAC) protocol data unit (MPDU) of which a transmission is imminent. In the case that it is determined that a medium is on use by a carrier sensing mechanism, the STA may determine the size of contention window (CW) using a random backoff algorithm, and perform a backoff procedure. In order to perform the backoff procedure, the STA may select a random value within the CW, and determine the backoff time based on the selected random value.
When a plurality of STAs trying to access a medium, the STA that has the shortest backoff time among a plurality of STAs may access the medium and the remaining STAs may interrupt the remaining backoff time and wait until the transmission of the STA that accesses the medium is completed. After the frame transmission of the STA that accesses the medium is completed, the remaining STAs may perform contention with the remaining backoff time, and may acquire transmission resources. In such a way, in the conventional WLAN system, a single STA performs transmission or reception of the frame with an AP by occupying total transmission resources through a single channel.